LIBPSX(3) Linux Programmer's Manual LIBPSX(3)
NAME
psx_syscall3, psx_syscall6, psx_set_sensitivity - POSIX semantics for
system calls
SYNOPSIS
#include <sys/psx_syscall.h>
long int psx_syscall3(long int syscall_nr, long int arg1, long int arg2, long int arg3);
long int psx_syscall6(long int syscall_nr, long int arg1, long int arg2, long int arg3, long int arg4, long int arg5, long int arg6);
int psx_set_sensitivity(psx_sensitivity_t sensitivity);
Link with one of these:
ld ... -lpsx -lpthread --wrap=pthread_create
gcc ... -lpsx -lpthread -Wl,-wrap,pthread_create
DESCRIPTION
The libpsx library attempts to fill a gap left by the pthreads(7) im-
plementation on Linux. To be compliant POSIX threads, via the nptl(7)
setxid mechanism glibc maintains consistent UID and GID credentials
amongst all of the threads associated with the current process. How-
ever, other credential state is not supported by this abstraction. To
support these extended kernel managed security attributes, libpsx pro-
vides a more generic pair of wrapping system call functions:
psx_syscall3() and psx_syscall6(). Like the setxid mechanism, the co-
ordination of thread state is mediated by a realtime signal. Whereas
the nptl:setxid mechanism uses signo=33 (which is hidden by glibc below
a redefined SIGRTMIN), libpsx inserts itself in the SIGSYS handler
stack. It goes to great length to be the first such handler but acts as
a pass-through for other SIGSYS uses.
A linker trick of wrapping the pthread_create() call with a psx thread
registration function is used to ensure libpsx can keep track of all
pthreads.
An inefficient macrology trick supports the psx_syscall() pseudo func-
tion which takes 1 to 7 arguments, depending on the needs of the
caller. The macrology pads out the call to actually use psx_syscall3()
or psx_syscall6() with zeros filling the missing arguments. While using
this in source code will make it appear clean, the actual code foot-
print is larger. You are encouraged to use the more explicit
psx_syscall3() and psx_syscall6() functions as needed.
psx_set_sensitivity() changes the behavior of the mirrored system
calls: PSX_IGNORE ensures that differences are ignored (the default be-
havior); PSX_WARNING prints a stderr notification about how the results
differ; and PSX_ERROR prints the error details and generates a SIGSYS
signal.
RETURN VALUE
The return value for system call functions is generally the value re-
turned by the kernel, or -1 in the case of an error. In such cases er-
rno(3) is set to the detailed error value. The psx_syscall3() and
psx_syscall6() functions attempt a single threaded system call and re-
turn immediately in the case of an error. Should this call succeed,
then the same system calls are executed from a signal handler on each
of the other threads of the process.
CONFORMING TO
The needs of libcap(3) for POSIX semantics of capability manipulation.
You can read more about why this is needed here:
https://sites.google.com/site/fullycapable/who-ordered-libpsx
REPORTING BUGS
The libpsx library is distributed from
https://sites.google.com/site/fullycapable/ where the release notes may
already cover recent issues. Please report newly discovered bugs via:
https://bugzilla.kernel.org/buglist.cgi?component=lib-
cap&list_id=1090757
SEE ALSO
libcap(3), pthreads(7) and nptl(7).
2021-12-12 LIBPSX(3)
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